Optical system

ABSTRACT

In preferred forms of the invention an array of MEMS mirrors or small mirrors inside an optical system operates closed-loop. These mirrors direct external source light, or internally generated light, onto an object—and detect light reflected from it onto a detector that senses the source. Local sensors measure mirror angles relative to the system. Sensor and detector outputs yield source location relative to the system. One preferred mode drives the MEMS mirrors, and field of view seen by the detector, in a raster, collecting a 2-D or 3-D image of the scanned region. Energy reaching the detector can be utilized to analyze object characteristics, or with an optional active distance-detecting module create 2- or 3-D images, based on the object&#39;s reflection of light back to the system. In some applications, a response can be generated. The invention can detect sources and locations for various applications.

Wholly incorporated by reference herein is coowned U.S. provisionalpatent application Ser. 60/433,301, whose priority benefit is herebyasserted.

RELATED DOCUMENTS

Closely related documents are other, coowned U.S. utility-patentdocuments and references—also incorporated by reference. Those documentsare in the names of:

-   -   Kane, provisional application Ser. 60/381,286, also incorporated        by reference in the provisional application that is mentioned        above;    -   Kane et al., application Ser. No. 10/142,654 “HIGH-SPEED,        LOW-POWER OPTICAL MODULATION APPARATUS AND METHOD”.

FIELD OF THE INVENTION

This invention relates generally to systems and methods forautomatically detecting light from an object, determining direction orother characteristics (such as distance, spectral properties, or animage) of the detected light or the object, and possibly responding tothe detected light.

BACKGROUND

Some conventional systems and methods for accomplishing these goals relyupon scan mirrors that receive signals from an object and relay theminto an aperture of an optical system—and, for response, converselyreceive signals from the optical-system aperture and return thosesignals toward the object. Some such systems and methods instead (oralso) rely upon gimbals that support and reorient the entire opticalsystem. Both approaches entail relatively high moments of inertia, andaccordingly large motors and elevated power requirements.

Such configurations require extremely adverse tradeoffs and compromisesbetween, on one hand, undesirably high cost and size, and on the otherhand structural weaknesses that lead to unreliability and even failure.For instance expensive custom parts and instrumentation are the rulerather than the exception, while some conventional devices havedimensions on the order of one to ten centimeters with mass of one toten or even hundreds of kilograms.

These are significant handicaps for—in particular—devices that may befor use in airplanes and satellites. Even in these cases, such drawbacksmight be acceptable if such systems provided superb performance, butunfortunately angular resolution in conventional systems of varioustypes is generally no better than two-thirds of a degree—sometimes ascoarse as ten degrees and more.

For example gimbal controls are most typically good to roughly onedegree or less, although some units capable of precision in tens ofmicroradians are available for millions of dollars each. Sensors usingfocal-plane arrays, e. g. quad cells, are typically precise to roughlyten degrees. Other nonmechanical systems include quad cells behindfisheye lenses.

The poor angular resolution and other performance limitations of suchsensors arise in part from use of fixed, very large sensor assemblies,typically quad cells, CCD or CMOS arrays, at a focal plane—with fixedfields of view. These components accordingly also suffer from limitedfields of regard. Furthermore the necessity for downloading into acomputer memory the massive volumes of data from multimegabyte sensorarrays makes the frame rate of these systems extremely slow.

In efforts to improve the field of regard, the large areal arrays aresometimes placed behind radically wide-angle lenses, even fish-eyelenses. This strategy, however, is counterproductive in that it onlycompounds the data-download problem, while also yielding intrinsicallycoarse angular resolution and very nonlinear angular mapping.

In other words these systems are squeezed between the need for highresolution and the need for broad field of regard; this squeeze comesdown to an all-but-prohibitive demand for dynamic range, or bandwidth.Data congestion, furthermore, is doubly problematic because in thesesystems the entire contents of every frame must be retrieved before thatframe can be searched for an optical source of interest.

One rather unnoticed contributor to inadequate dynamic range is thedirect relationship between gimbal angle or scan-mirror angle andexcursion of the beam in the external scanned volume. That relationshipis a natural one-to-one for a gimbal system, and one-to-two for arotating mirror. Since the direct effect of mechanical rotation isrelatively slow for gimbals, and relatively limited in overall angularexcursion for scan mirrors, the external beam-angle excursion is eitherslow or limited, or both.

In attempts to mitigate low resolution and frame rate, some workers haveproposed to substitute a so-called “position-sensing detector” (PSD) forthe commonly used larger arrays. The advantage of a PSD—which is aunitary device, not an array—is that it inherently locates and reportsposition of only a detected optical source, not an entire scene, andthus requires download of only a far smaller amount of data.

Another inherent advantage of a PSD is that it provides a continuous,analog positional readout, intrinsically yielding extremely highresolution. The report from an array is instead quantized by the pixel(or “aliasing”) effect that is central to any kind of array detection.

The PSD reports position on its own sensitive surface, in units ofdistance from its nominal center along two orthogonal axes. To findangular mapping, typically these off-center coordinates are divided bythe focal length of a final focusing element.

Unfortunately these reported distances and therefore the angular mappingof a PSD are nonlinear, to the extent of several percent at the PSDedges—aggravating the analogous handicap introduced by a fish-eye orother wide-angle lens—and are also temperature sensitive. The detectormay report accurately that an optical source has been sensed, but failto report accurately where that object is, unless it is near the nominalcenter, or origin of coordinates.

It might be supposed—although in actuality this supposition is wellbeyond the present state of the art, and artisans of ordinary skill—thatsuch a system could be quickly turned to look directly at the candidateobject, for a more-accurate assessment of position. In any conventionaldetector, however, this solution is impractical due to the lumberingresponse of an associated gimbal system, or even of a scan mirror thatis redirecting the light into the detector aperture.

Often it is desirable to know something more about an optical sourcethat has been noticed—the character of the light itself, and anyintelligence signal that may be impressed upon that light. Accuratedetermination of wavelength and frequency modulation information, as maybe gleaned from the foregoing discussion, is beyond the capabilities ofthese systems. Similarly infeasible is any exploration of physicalobjects that may be associated with the optical source.

The intractability of attempting to operate with such systems may beclarified by consideration of some practical situations which call foruse of optical sensors. In most applications a person or an apparatuspoints a light source toward, most typically, some sort of vehicle—toguide an object in an attempt to rendezvous with the vehicle. Commonlythe intention is adversarial, as for example damage to the vehicle;while the optical-sensor apparatus is mounted on the vehicle and itspurpose is to detect the presence of the light beam and initiate someprotective response.

Such response, usually intended to produce confusion as to the exactlocation of the vehicle, sometimes takes the form of returning aliterally blinding flash of light toward the person or apparatus that ispointing the original source, to temporarily dazzle and confuse thatsource-controlling entity. Alternatively a response can be to eject fromthe vehicle many particles that strongly reflect the guide light, toinstead confuse directional-control mechanisms of the moving object.Accompanying either of these may be an entirely different kind ofresponse, namely an effort to disable the source-pointing person orapparatus, or the object. Such a disabling response, directed toward theobject or source, may take the form of either a physical article or ofpowerful radiation. Still another desirable kind of response would beinvestigatory, i. e. determining the character of the guide beam or ofthe guided object; such information can be used to determine and reportthe nature of the guiding system itself, either for purposes ofimmediate efforts to confuse and avoid or for future protective-designwork.

The person or apparatus pointing the source may be adjacent to theinitial position of the object. In a sense this is the easiest case fromthe standpoint of protective response, because the source can be treatedas a beacon for guidance of a disabling response that eliminates boththe light source and the object—if the response is sufficiently prompt,so that the source and object are still not only in-line but alsorelatively close together. In another sense, however, this is adifficult case from the standpoint of confusion, because the object mayhave been designed to look (for its guidance) backward at the sourcerather than forward at the vehicle—in which event the ejection ofreflecting particles cannot confuse the directional-control mechanismsof the object, as long as the pointing entity can keep the vehicle inview.

The person or apparatus pointing the source may, however, instead be ata different position—off to the side from the path of the object, andfrom a line between the source and the object. In this event, disablingboth the source and object with a single response is not possible; butat least confusion can be more-readily produced since the object isnecessarily designed to look forward at the vehicle, so that either thedazzling or the decoy-particle strategy, or both, can be effective.

One type of movable-mirror device that is known in various kinds ofoptical-detection systems is a single scan mirror of about 25 or 30 mmor more, consistent with the earlier statement of dimensions forconventional systems. Such mirrors are too bulky and heavy to overcomethe previously discussed problems of response speed.

Another type of known movable-mirror device is a spinning cylinder withmultiple mirrors carried on its outer surface. Such a polyhedralconstruction does provide a movable mirror, sometimes disposed along anoptical path between a detector and an entrance aperture. Dimensions ofeach of the mirrors in such a device are typically in the tens ofmillimeters, also consistent with the previous indication ofrepresentative dimensions for conventional systems. Hence the overalldevice and even the individual mirrors are too big and heavy to free theoptical-detection art from the response-speed and related limitationsdiscussed above. These mirror wheels are ordinarily made to spincontinuously; hence the individual mirrors of such an array lackindependent maneuverability for customized control movements.Accordingly they are poorly suited for practical use in rapid detectionand tracking of a particular source object.

Also of interest are telescopes—including astronomicaltelescopes—particularly of the type that has a movable mirror positionedbetween an entrance aperture and a detector. For present purposes,however, any interest in such devices is academic, as the movablecomponents are relatively huge and far too massive to be useful in anyrapid-response system. Even more relevant is the typical limitation offield of view, in telescopes, to less than ten degrees.

Smaller deformable mirrors, too, are sometimes placed within opticalsystems in positions such as just described. A device of this typegenerally comprises a continuous reflective membrane that iscontrollably bent and distorted to correct wavefront errors. Suchmirrors are typically at least 20 to 30 mm across.

Another type of known moving-mirror device, never heretofore associatedwith the field of optical-source detection that is under considerationhere, is called a “microelectromechanical system” (MEMS) mirror. Suchdevices, introduced some years ago by the Texas Instruments Company, andmore recently in versions produced by Lucent Technologies and called an“optical switch”, most commonly take the form of arrays of very smallmirrors—each on the order of ten to 500 microns across. At least inprinciple individual mirrors can be made available in the same format.In use these devices, while some are capable of continuous positionalcontrol, are most often only bistable, used for switching in opticalinformation networks and also in an image-projection system for personalcomputers.

Another familiar optical device not previously associated with thepresent field, are afocal lens packages used e. g. as lens focal-lengthextenders. These are commonplace in ordinary cameras.

Almost all the optical devices discussed above, and most conspicuouslythe astronomical ones and MEMS devices, are known only in differentfields from the present invention.

As can now be seen, the related art fails to resolve the previouslydescribed problems. The efforts outlined above, although praiseworthy,leave room for considerable refinement.

SUMMARY OF THE DISCLOSURE

The present invention introduces such refinement. The invention hasseveral major facets or aspects, which can be usedindependently—although, to best optimize enjoyment of their advantages,certain of these aspects or facets are best practiced (andmost-preferably practiced) in conjunction together.

In preferred embodiments of its first major independent facet or aspect,the invention is an optical system for dynamically determining radiationcharacteristics, including associated angular direction, of an externalarticle in a volume outside the system. The optical system includes anoptical detector and an entrance aperture.

It also includes at least one mirror for causing the detector to addressvarying portions of the volume outside the optical system. The “at leastone mirror” is disposed along an optical path between the detector andthe entrance aperture, and is rotatable about plural axes—and eachmirror of the “at least one” has dimensions in a range from thirtymicrons to five millimeters.

The foregoing may represent a description or definition of the firstaspect or facet of the invention in its broadest or most general form.Even as couched in these broad terms, however, it can be seen that thisfacet of the invention importantly advances the art.

The specified mirror position, between detector and aperture, can alsobe described as within or inside the optical system. Steering theincoming radiation beam (i. e., maneuvering the sensitivity direction ofthe system) from within the system produces opportunities to obtain verylarge optical leverage, as compared with turning the entire system ongimbals or steering with mirrors external to the system. That is, theangle through which the beam outside the system turns can be made muchlarger than that through which the beam inside the system turns. (Thelatter angle is twice that through which the mirror turns.)

In addition the beam cross-section inside the optical system isgenerally smaller than outside. Hence smaller, lighter optical elementscan be used, and this in turn means greater response speed with lesspower.

As mentioned previously, the examples of earlier optical systems usinginternal mirror positioning are so-called “nonanalogous arts”. In otherwords they are not in the same field as the present invention.

Although the first major aspect of the invention thus significantlyadvances the art, nevertheless to optimize enjoyment of its benefitspreferably the invention is practiced in conjunction with certainadditional features or characteristics. In particular, preferably eachmirror of the at least one mirror is a microelectromechanical mirror.

Also preferably the optical system further includes a lens assemblydisposed at the aperture to amplify the varying introduced by the atleast one mirror. If this preference is observed, then it is furtherpreferable that the lens assembly not focus the external article on anysolid element of the optical system.

Other basic preferences are that the system further include some meansfor automatically servocontrolling the at least one mirror to perform araster scan of the volume; and that the at least one mirror be an arrayof mirrors having the dimensions stated.

Yet another basic preference arises if the external article comprises aradiation source of a particular type, the characteristics compriseexistence and presence of the source, and the optical system is fordetecting the source and determining its angular location. In this caseit is preferred that the optical detector be a detector for theradiation from the source of the particular type. If this preference isobserved, then a subpreference is that the system further include somemeans for automatically responding to the detector by activelyservocontrolling the at least one mirror to substantially center animage of a detected source on the detector.

A still further additional-tier subpreference, applicable when suchservocontrol is in use, is that the responding means comprise some meansfor continuing to servocontrol the at least one mirror to track thealready-detected source substantially at the detector center.

Reverting to the basic preference of a particular radiation-source type,two alternative subpreferences are that the detector be either aposition-sensing detector (PSD) or a quad cell. In these cases it isalso preferable that the system further include some means forsubstituting a detector array for the detector, to image thealready-detected source or associated objects, or both. Here the conceptof “substituting” an array for the detector refers to a function that issubstantially immediate, after detection, and that encompasses e.g.optically switching the array into place while the already-existingapparatus continues to function. Thus this is not meant to suggestbuilding an apparatus with, initially, an array instead of a PSD or quadcell. (Certain other configurations discussed in this document, however,do relate to building such an apparatus.)

Yet another subpreference to the basic particular-source preference isthat the system further include some means for automatically directing aresponse toward the detected source or an object associated therewith,or both. If this subpreference is observed, then still furtherpreferably the response-directing means include some means for emittinga beam of radiation that uses the entrance aperture as an exit aperture,i. e. sharing the entrance aperture with the radiation from the source.In one preferred version of this aperture-sharing form of the invention,the response-directing means include some means for emitting a rangingbeam pulse.

Still another basic preference, relative to the first major aspect ofthe invention, is applicable when the external article comprises aradiation source, the characteristics include spectral properties ofradiation from the source, and the optical system is for determining theradiation spectrum of the source as a function of angular direction.Under these circumstances, preferably the optical detector is aspectrometer.

When the detector is a spectrometer, three further preferences are that(1) the system further include some means for automatically controllingthe at least one mirror to perform a spectrometric raster scan of thespectrometer over the source; (2) the spectrometer be an interferometricspectrometer, or grating- and/or prism-based spectrometer; and (3)—ifthe characteristics further include at least one temporal modulationpattern of radiation from the source—the system further include somemeans for analyzing the radiation to determine the at least one temporalmodulation pattern as a function of angular direction. In thislast-mentioned third case, also preferably the system further includessome means for generating a beam of radiation having the determinedspectrum and the determined at least one temporal modulation pattern.Still another subpreference is that the detected spectral and temporalmodulation characteristics of the received radiation be immediatelytransmitted to a remote station, e. g. a companion host or a basestation, or both, for possible use in later avoidance of guidance bysimilar beams, particularly at other hosts. Ordinarily this informationis preferably transmitted in the form of interpreted and encoded data,although for some applications it is advantageous to simply relay e. g.the original modulation pattern as such.

Two additional basic preferences will be taken up now. One of these isapplicable if the external article comprises an object or scene, and thecharacteristics include an image of the object or scene, and the opticalsystem is for forming the image. In this case it is preferable that theoptical detector be an imager detector—in other words, a detector thatis used as part of an imager, or as an imager. This is one case, such aswas mentioned earlier, in which the system may actually be initiallybuilt with an imager detector, rather than necessarily involvingsubstitution of such a detector, during operation, for aposition-sensing or other directionality detector. In fact thepreference under consideration now encompasses both an as-built systemwith imager detector, and a system that can substitute such a detectorfor a directionality device during operation.

It is also preferable that the system further include some means forautomatically controlling the at least one mirror to perform an imagingraster scan of the detector over the object or scene. The term “raster”here is not limited to the traditional video scan of e. g. a serpentinescan pattern, but rather is to be understood in its broader sense of apredetermined pattern of scanning to cover substantially an entire area.In fact a particularly important subpreference is that the raster be aspiraling scan pattern.

Other subpreferences are that the detector be an infrared detector, or avisible-light detector, or a single-pixel detector, or a detector thathas a few pixels. As will be appreciated, some of these are mutuallyexclusive.

The final basic preference to be considered here, in relation to thefirst main independent aspect or facet of the invention, is applicableif the external article comprises an object or scene of interest, andthe characteristics comprise distance data for different portions,respectively, of the object or scene, and the optical system is forforming the distance data. In this case preferably the optical detectorincludes a distance-determining receiver. For background of suchtechnology, and some other related technology, these patents andpublications are wholly incorporated by reference: Griffis et al., U.S.patent application Ser. No. 10/426,907, “Compact economical lidarsystem”; Bowker et al., application Ser. No. 09/125,259,“Confocal-reflection streak lidar apparatus with strip-shapedphotocathode, for applications at a wide range of scales”; and otherscited therein. Additional related documents are technical articles andpamphlets including: Philip J. Bos, “Liquid crystal based optical phasedarray for steering lasers”, Kent State University, PresentationMaterials; Brooker, Graham et al., “Millimetre waves for robotics” Proc.2001 Australian Conference on Robotics and Automation, (Sydney; 14-15Nov. 2001); and Bruce Winker, “Liquid crystal agile beam steering”,Rockwell Science Center (Thousand Oaks, Calif.; Aug. 8, 2000). Onceagain the preference under consideration, involving distanceinformation, encompasses a set of configurations that either can beso-built at the outset or can entail substitution of thedistance-determining device for a directionality detector duringoperation.

Three subpreferences are particularly noteworthy: preferably (1) thedistance-determining receiver includes a single-pixel receiver, and thesystem further includes some means for controlling the at least onemirror to perform a raster scan of the single-pixel receiver over theobject or scene; (2) the distance-determining system includes a receiverhaving a few pixels, and the system further includes some means forcontrolling the at least one mirror to perform a raster scan of thefew-pixels receiver over the object or scene; and (3) the system furtherincludes a distance-determining transmitter that uses the entranceaperture as also an exit aperture for a pulsed excitation beam.

In preferred embodiments of its second major independent facet oraspect, the invention is an optical system for impairing function orstructural integrity of an external article in a volume outside theoptical system—including controlled effect upon the article as afunction of angular direction. The optical system includes a laser, andan exit aperture.

It also includes at least one mirror for causing the laser to addressvarying portions of the volume outside the optical system, to impairfunction or structural integrity of corresponding portions of theexternal article. The “at least one mirror” is disposed along an opticalpath between the laser and the exit aperture, and rotatable about pluralaxes; and each mirror of the “at least one” has dimensions in a rangefrom thirty microns to five millimeters.

The foregoing may represent a description or definition of the secondaspect or facet of the invention in its broadest or most general form.Even as couched in these broad terms, however, it can be seen that thisfacet of the invention importantly advances the art.

In particular, the advantages of the mirror placement and size recitedhere are closely analogous to those identified above for the firstaspect or facet of the invention. As people skilled in this fieldappreciate, many important characteristics of optical systems areindependent of light-propagation direction through the systems—i. e., ofwhether the system is one that receives and responds to radiation, orone that generates and transmits the radiation.

Although the second major aspect of the invention thus significantlyadvances the art, nevertheless to optimize enjoyment of its benefitspreferably the invention is practiced in conjunction with certainadditional features or characteristics. In particular, preferably thesystem further includes some means for using the exit aperture as anentrance aperture, to receive a sensing beam from an optical source inthe volume.

Another preference is that the system further include some means forcontrolling the at least one mirror to perform a raster scan of thelaser over the external article. As people skilled in this field willrecognize, many or most of the preferences introduced above for thefirst main receptor-system aspect of the invention also have analogsapplicable to this second major transmitter-system facet of theinvention.

One further basic preference is that the optical system include avibration sensor, and some means for applying information from thesensor to stabilize lines of sight of the small movable mirrors.

In preferred embodiments of its third major independent facet or aspect,the invention is apparatus for dynamically detecting and determiningradiation characteristics, including associated angular direction, of anarticle outside the apparatus. The apparatus includes an opticaldetector.

The apparatus also includes at least one microelectromechanical mirrorfor causing the detector to address varying portions of the article. Theterm “microelectromechanical mirror” is verbal shorthand for“microelectromechanical system mirror”, or “MEMS mirror”, establishedcommercial products introduced by the Texas Instruments Company andLucent Technologies, among others.

The foregoing may represent a description or definition of the thirdaspect or facet of the invention in its broadest or most general form.Even as couched in these broad terms, however, it can be seen that thisfacet of the invention importantly advances the art.

In particular, as MEMS mirrors with their associated actuators areestablished products and available in a variety of configurations andsizes, they can make extremely rapid and nimble steering of a detectionbeam very straightforward. Response time of the individual mirrors isexcellent, due to their availability with remarkably low mass and size.Continuous maneuverability about two orthogonal axes is not only smoothand orderly over the full range of operation, but also highlyreproducible—so that angular position as a function of mirror positionfeedback signals (e. g. from embedded capacitive sensors) can becalibrated and thereafter all mirror angles known very precisely fromthe instantaneous feedback signals.

Yet as mentioned earlier, these devices are ordinarily used in only abinary or bipolar mode for optical switching in communications and incomputerized image-projection systems. They have not been used inspatially-continuous positional control of optical beams. As will beseen, some of the most highly preferred embodiments of the invention areimplemented through the use of feedback servocontrol in which the mirrorposition feedback signals are used as the positional readouts for theinitially unknown source location that is desired.

As previously noted, plural and especially multiple mirrors areparticularly useful in scanning different sectors concurrently. This hasthe benefit of track different sources or other articles at the sametime. In addition several mirrors have, in the aggregate, greatereffective energy-collecting power than a single mirror.

Although the third major aspect of the invention thus significantlyadvances the art, nevertheless to optimize enjoyment of its benefitspreferably the invention is practiced in conjunction with certainadditional features or characteristics. From the discussion thatfollows, it will be noted that some of these preferences are closelyrelated to those enumerated above for the first main aspect of theinvention.

In particular, preferably the optical system further includes a lensassembly disposed at the aperture to amplify the varying introduced bythe at least one microelectromechanical mirror. If this preference isobserved, then a further preference is that the lens assembly be“afocal”—i. e., that it not focus the external article on any solidelement of the optical system.

Another basic preference is that the system include some means forautomatically servocontrolling the at least one microelectromechanicalmirror to perform a raster scan of the volume. The previous note aboutthe definition of “raster” is applicable here as well. Another basicpreference is that the at least one microelectromechanical mirror be anarray of microelectromechanical mirrors.

Yet another basic preference is applicable if the external articlecomprises a radiation source of a particular type, the characteristicscomprise existence and presence of the source, and the optical system isfor detecting the source and determining its angular location. In thiscase preferably the optical detector is a detector for radiation fromthe source of the particular type.

When this particular-source-type preference is in use, then asubpreference is that the optical system further include some means forautomatically responding to the detector by actively servocontrollingthe at least one microelectromechanical mirror to substantially centeran image of a detected source on the detector. When this subpreferencein turn is observed, then a still further preference is that theresponding means include some means for continuing to servocontrol theat least one microelectromechanical mirror to track the already-detectedsource substantially at the detector center. As mentioned above, theseservocontrol embodiments of the invention are powerful in their abilityto yield stable and precise angular readouts, from the typicallybuilt-in mirror position-sensor feedback signals—and these output data,particularly for angles well off-axis, are far more precise thanavailable from off-axis readings of typically temperature-sensitiveoptical detectors.

Another subpreference nonetheless is that the detector be aposition-sensing detector (PSD). These devices enable the optical systemto determine off-axis direction and approximate magnitude, directly fromPSD signals—and these signals can therefore be used for proportional,integral and/or derivative servocontrol, if desired, in the feedbackloop. This type of servosystem accordingly can operated in a dampedmode, especially valuable when the overall system is called upon tooperate at the margins of its dynamic-response capability. If apreferred PSD is in use, then a still further preference is that thesystem further include some means for substituting a detector array forthe detector, to image the already-detected source or associatedobjects, or both.

Yet another subpreference, when the basic particular-source-typepreference is employed, is that the system further include some meansfor automatically directing a response toward the detected source or anobject associated therewith, or both. In this case it is still furtherpreferable that the response-directing means include some means foremitting a beam of radiation that uses the entrance aperture as an exitaperture, sharing the entrance aperture with the radiation from thesource.

Another basic preference, with respect to the third main facet or aspectof the invention, is applicable if the external article comprises aradiation source, the characteristics include spectral properties ofradiation from the source, and the optical system is for determining theradiation spectrum of the source as a function of angular direction. Inthis case, preferably the optical detector is a spectrometer.

When this basic preference is observed, then again analogoussubpreferences come into play. It is preferred that the system furtherinclude some means for automatically controlling the at least onemicroelectromechanical mirror to perform a spectrometric raster scan ofthe spectrometer over the source.

If the characteristics further include at least one modulation patternof radiation from the source, then it is also preferable that the systemfurther include some means for analyzing the radiation to determine theat least one modulation pattern as a function of angular direction. Inthis event it is still further preferable that the system include somemeans for generating a beam of radiation having the determined spectrumand the determined at least one temporal modulation pattern. Asmentioned in relation to the first major aspect of the invention, stillanother subpreference is that the detected spectral and temporalmodulation characteristics of the received radiation be transmitted to aremote station.

Yet another set of preferences arises if the external article comprisesan object or scene, the characteristics comprise an image of the objector scene, and the optical system is for forming the image. In this casepreferably the optical detector is an imager detector; and the systemalso includes some means for automatically controlling the at least onemicroelectromechanical mirror to perform an imaging raster scan (onceagain as broadly defined) of the detector over the object or scene.

Still another basic preference arises if the external article comprisesan object or scene, the characteristics comprise range data fordifferent portions, respectively, of the object or scene, and theoptical system is for forming the range data. Here preferably theoptical detector includes a distance-determining receiver.

In this case it is preferable that the receiver include a single-pixelreceiver; and that the system include some means for controlling the atleast one mirror to perform a raster scan of the receiver over theobject or scene. It is furthermore preferred that the system include adistance-determining transmitter which uses the entrance aperture asalso an exit aperture for a pulsed excitation beam.

One further basic preference, mentioned earlier in relation to the firstmain aspect of the invention, is that the optical system include avibration sensor, and some means for applying information from thatsensor to stabilize lines of sight of the microelectromechanicalmirrors.

In preferred embodiments of its fourth major independent facet oraspect, the invention is an optical system for impairing function orstructural integrity of an article outside the apparatus—particularlyincluding controlled effect upon the article as a function of angulardirection. The optical system includes a laser, and an exit aperture.

The system also includes at least one microelectromechanical mirror forcausing the laser to address varying portions of the article, to impairfunction or structural integrity of corresponding portions of thatarticle.

The foregoing may represent a description or definition of the fourthaspect or facet of the invention in its broadest or most general form.Even as couched in these broad terms, however, it can be seen that thisfacet of the invention importantly advances the art.

In particular, this facet of the invention extends the above-mentionedextraordinary benefits of MEMS mirrors in a beam-steering system, fromthe environment of optical-source detection into the context ofprojecting a disruptive beam.

Although the fourth major aspect of the invention thus significantlyadvances the art, nevertheless to optimize enjoyment of its benefitspreferably the invention is practiced in conjunction with certainadditional features or characteristics. In particular, preferably theoptical system further include some means for controlling the at leastone mirror to perform a raster scan of the laser over the externalarticle. Most of the other preferences stated above forearlier-introduced main facets of the invention are applicable here too.

In preferred embodiments of its fifth major independent facet or aspect,the invention is apparatus for detecting and determining angulardirection of radiation from an external source. The apparatus includesan optical system having a detector component that reports relativelocation of incident radiation on a sensitive surface of the detectorcomponent.

The apparatus also includes at least one mirror for causing the detectorcomponent to address varying portions of a volume outside the opticalsystem. In addition the apparatus also includes some means forautomatically responding to the detector component by activelyservocontrolling the at least one mirror to substantially center animage of a detected source on the detector component.

The foregoing may represent a description or definition of the fifthaspect or facet of the invention in its broadest or most general form.Even as couched in these broad terms, however, it can be seen that thisfacet of the invention importantly advances the art.

In particular, by servocentering the source image on the directionalitydetector, the system essentially neutralizes any off-axis errors orinstabilities which afflict that detector component. This fifth aspectof the invention, like certain preferences of earlier-described facetsof the invention, relies upon signal levels associated with theservocontrol function—rather than directly upon the detector signals—toobtain a stable, precise measure of source location.

Although the fifth major aspect of the invention thus significantlyadvances the art, nevertheless to optimize enjoyment of its benefitspreferably the invention is practiced in conjunction with certainadditional features or characteristics. Several of these preferences arein the nature of mutually exclusive options.

In particular, preferably the detector component includes aposition-sensing detector (PSD); or includes a quad cell; or includes afocal-plane array—but in this latter case, preferably the detectorcomponent further includes a processor operating a program for analyzingdata from the focal-plane array.

Another basic preference is that each mirror of the at least one mirrorbe a microelectromechanical mirror. Yet another preference is that theat least one mirror be an array of microelectromechanical mirrors.

Where plural and particularly multiple mirrors are in use, rays can allbe made parallel—or different sectors can look in different directions.This has the benefit of being able to track different sources or otherarticles simultaneously. Also, a group of mirrors has a greatereffective aperture for energy collection.

Still another basic preference is that the apparatus further include anoptical-system aperture, and a lens disposed at the aperture to amplifythe varying introduced by the at least one mirror. In this case asubpreference is that the lens at the aperture not focus the radiationfrom the external source.

Yet another basic preference is that the apparatus further include somemeans for automatically controlling the at least one mirror to perform araster scan of the volume. In this case a subpreference is that theservocontrolling means continue to servocontrol the at least one mirrorto track the already-detected source substantially at the detectorcenter.

Another basic preference is that the apparatus further include somemeans for substituting a detector array for the detector, to image thealready-detected source or associated objects, or both. The meaning of“substituting” here is as discussed earlier.

A final basic preference, with regard to the fifth main aspect of theinvention that is under consideration, is that the apparatus furtherinclude some means for automatically directing a response toward thedetected source or an object associated therewith, or both. In this casea subpreference is that the apparatus further include an entranceaperture for collecting radiation from the source; and that theresponse-directing means include some means for emitting a beam ofradiation that uses the entrance aperture as an exit aperture, sharingthe entrance aperture with the radiation from the source. A parallelsubpreference is that the response-directing means include some meansfor emitting a ranging beam pulse.

In preferred embodiments of its sixth major independent facet or aspect,the invention is an optical system for varying angular direction,outside the optical system, of a transmitted or received beam ofcollimated radiation. The optical system includes a physical-interactionstage where the transmitted beam is generated, or the received beam isintercepted by utilization means.

The system also includes at least one movable mirror for varyingdirection, outside the optical system, of the beam—by rotation of beamdirection at the mirror through a particular angle. In addition thesystem includes some means for multiplying the particular angle by adesired factor; and the at least one movable mirror is disposed along anoptical path between these angle-multiplying means and thephysical-interaction stage.

The multiplying means include plural focal elements, in series, thathave respectively different focal lengths. The desired factor is equalto a ratio of the focal lengths.

The foregoing may represent a description or definition of the sixthaspect or facet of the invention in its broadest or most general form.Even as couched in these broad terms, however, it can be seen that thisfacet of the invention importantly advances the art.

In particular, the beam-angle multiplication feature enables a verybroad beam sweep, or scanning range, outside the optical system inresponse to a relatively modest angular excursion of the movable mirrorinside the system. This broad sweep is achieved without sacrifice ofangular sensitivity or precision in mirror position; hence this systemmakes a major contribution to dynamic range in detected angle.

Although the sixth major aspect of the invention thus significantlyadvances the art, nevertheless to optimize enjoyment of its benefitspreferably the invention is practiced in conjunction with certainadditional features or characteristics. In particular, preferably thefocal elements are lenses.

Also preferably the focal elements focus the collimated beam to avirtual, substantially point image and form another collimated beam fromthe substantially point image. If this basic preference is observed,then a subpreference is that the focal elements form the virtual,substantially point image between the focal elements.

Three other basic preferences may be noted. First, preferably the pluralfocal elements are disposed between the movable mirror and:

-   -   an exit aperture, if the beam is a transmitted beam; or    -   an entrance aperture, if the beam is a received beam.

Second, most preferably the focal lengths are in the ratio ofapproximately 1:3 or 3:1, and accordingly the desired factor isapproximately 3 or 1/3, respectively. More generally, usable ratios fallrepresentatively in the range of 1:2 to 1:4, yielding factors between 4(or 1/4) and 2 (or 1/2).

Third, the plural focal elements comprise more than two focal elements,and the ratio of focal lengths equals a ratio of (1) a first compositeeffective focal length of a subgroup of two or more of the focalelements, and (2) an effective focal length of all remaining focalelements.

It is to be understood that the foregoing enumeration of preferences isintended to be representative, not exhaustive. Accordingly manypreferred forms of the invention set forth in the following detaileddescription or claims are within the scope of the present invention.

All of the foregoing operational principles and advantages of theinvention will be more fully appreciated upon consideration of thefollowing detailed description, with reference to the appended drawings,of which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram, with most portions symbolically in sideelevation but certain other portions (an aperture-lens assembly 14 and alens/detector assembly 22) symbolically in isometric projection, of abasic first function—namely, a detection function—for preferredapparatus embodiments of the invention;

FIG. 2 is a like diagram showing an extension of the preferred apparatusembodiments to encompass a second function, namely optical analysis;

FIG. 3 is another like diagram but now showing a further extension toencompass dual forms of yet a third function, namely response;

FIG. 4 is a multiapplication block diagram representing apparatus andprocedures, using the apparatus embodiments of FIGS. 1 through 3 for theabove-mentioned and still other functions, and in a number of variegatedapplications;

FIG. 5 is a diagram generally like FIGS. 1 through 3 but with the lensand detector assemblies 14, 22 enlarged for presentation of details; and

FIG. 6 is a diagram conceptually representing a spiral-scanning rasterpattern for use in any of the FIG. 1 through FIG. 5 systems and methods.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In preferred embodiments, the invention provides a low-cost sensorsystem 10 (FIG. 1) capable of detecting and locating active illuminationsources—or objects illuminated by such sources. In some preferredembodiments (FIGS. 2 through 4), the sensor system of the invention canalso respond to the detected light source by returning a light beam 38(FIG. 3) or an object, and in some cases by initiating adistance-determining or other investigation (Function 4, FIG. 4) of thesource or objects associated with the source.

In particularly preferred embodiments, initial detection of a radiationsource or illuminated object is qualified by filters that implementexpectations as to the characteristics of such sources or objects thatare of interest. For instance, when anticipated sources are infrared, orare in other particular spectral regions, spectral filters are placed atconvenient positions in the optical path—usually but not necessarilyassociated with the fold mirror 21, and in particular taking the form ofbandpass optical reflection/transmission filters.

As mentioned elsewhere in this document, for various purposes the foldmirror can be advantageously implemented as a beam splitter, andincident-beam selectivity is simply an additional one of such purposes.In such arrangements, if it is preferable that certain spectralcomponents of the beam not pass to the primary directionality detector24, a dichroic or other bandpass or bandblocking filter can be used, asan alternative to a fold mirror 21. The filter transmits these undesiredcomponents to a radiation sink or auxiliary detection system 55, whilereflecting the desired radiation components to the detector—orconversely, depending on preferred system configuration.

Such advance filtering is not limited to spectral characteristics.Merely by way of example, if anticipated sources are modulatedtemporally, the signal 25 from the optoelectronic detector 24 isadvantageously filtered electronically 56 to exclude d. c. sources orsources having no significant bandwidth activity above a specificthreshold frequency—or, more restrictively, to pass only a. c. signalshaving a particular specified modulation pattern or class of patterns.

Ideally the system detector 24 is a PSD, which has the ability to reportpositional coordinates ΔX, ΔY (on the PSD's own surface, FIG. 5) of animpinging optical beam from a source 1 in a region without the necessityof scanning the region. As noted elsewhere in this document, it is alsonecessary to determine the mirror position. From these data and knowncharacteristics of the associated optics, as explained above, angularposition θ_(X), θ_(Y) of the source is readily calculated.

As mentioned earlier, however, a PSD is nonlinear and temperaturesensitive when measuring large off-axis coordinates ΔX, ΔY and thusangles θ_(X), θ_(Y). These drawbacks are neutralized, in preferred formsof the present invention, by operating in a null-balance mode asdetailed below—so that the system relies on the PSD primarily only todetermine whether the source is off axis and, if so, then in whichdirection; and not for quantitative reporting of large off-axiscoordinates or their associated angles.

After the sensor system (including the arithmetic preprocessingmentioned earlier) has determined initial values for the incident anglesθ_(X), θ_(Y), the system very rapidly servocontrols itself to keepincident rays 13 at the center of the detector field. Most preferablysuch servocontrol 27 is implemented by one or moremicroelectromechanical (MEMS) mirrors 15 disposed inside the opticalsystem 10, i. e. along the optical path between the detector 24 and thecollecting aperture 14, 45 (FIG. 5) of the system.

Such mirrors have extraordinarily low mass and inertia, andcorresponding extremely high response speed—thus obviating the problemof sluggish response in earlier systems. Placing the mirror or mirrorsinside the system gains yet further advantages of angular displacementspeed, in the visible volume 11 of space outside the optical system,particularly if a lens 45 is placed at the aperture to optically magnifythe angular displacement of the mirrors.

This particular arrangement for servocontrol of the incoming light, tocenter the beam on the detector, is particularly advantageous when usinga PSD. Whereas that type of detector measures large off-axis anglessomewhat inaccurately, the system is easily made extremely accurate inmeasuring the angular correction 28 applied by the MEMS system to bringthe source to the central, null position.

Throughout most of this document, for purposes of simplicity thenotation “θ_(X), θ_(Y)” has been used to represent both the off-axisangle of the beam 13 (FIG. 1) and the mirror-orientation 16 signals 28relative to nominal or rest positions of the mirror or mirrors 15. Aswill be understood, these two different sets of angles 13, 28 are not atall the same—but when the system has servocontrolled itself to null theincident beam at the center of the detector 24, the two sets are relatedby straightforward transforms. Such transforms include the magnificationfactor introduced by the afocal package 14, as discussed at lengthelsewhere in this document, and also include the local calibration ofthe mirror actuator-stem positions relative to an internal standard, andalso distortion in the afocal array 14 as well as the final focusingoptic 23, and so forth.

The PSD itself can effectively monitor a far larger angular region 11than it can image. This is a major advantage never fully exploited inconventional systems because of failure to use internal mirrors, or verysmall mirrors, and because of failure to servo the input source to areproducible centerpoint on the detector.

Nevertheless a still further major advantage is gained by rasterscanning 16 the PSD. The basic principle behind this is that the systemviews a small part of the field of regard at any instant in time, yetexpands its coverage by searching for incident rays, thereby coveringthe entire field of regard 11. As will be seen, practical field of viewusing the various forms of the invention can range, representatively,from 20° to 180°.

This combination of the intrinsic angular-dynamic-range advantage of thePSD with the multiplicative advantage of a raster scan yields anenormous bandwidth, or bit depth, in overall determination ofoptical-source angular location θ_(X), θ_(Y). Moreover, once a lightsource 1 is detected and the MEMS mirrors operated by a processor 26 tocenter the source in the detector field, advantageously the processorsends the MEMS mirrors further signals to continue searching/scanning 16in the general area of the detected rays—without losing the benefit ofhaving the source near the detector center, where moderate angularaccuracy is available. (Alternatively the native angular range of thePSD can be used for this purpose without additional mirror scanning.)

The optical system has been successfully servocontrolled to an incidentray when both coordinates ΔX and ΔY (FIG. 5) of the ray on the sensitivedetector surface are zero as measured by the two-dimensional (“2-D”)detector assembly (or in the case of a 1-D detector, when ΔX or ΔY iszero and the scan-mirror positions are noted) Once the system isservoing to the incident ray, as noted above it can function todetermine not only angular location of the incident ray but also itswavelength λ and coded temporal modulation f(t); or can direct similaror different light rays 35-38 (FIG. 3) opposite the incident rays 13along the same path, or laterally 43 with respect to that path—forcommunications, distance determination, optical enhancement or otherpurposes. In the case of light rays received from an adversary forguiding an object with destructive intent, an auxiliary laser 42 can bedirected 41 to emit a very bright beam 43 of identical wavelength λ andtemporal modulation f(t) onto a nearby (but progressively diverging)surface. This arrangement can closely mimic the original beam but in adifferent guiding location, and thereby draw off the object from theintended destination.

Various arrangements can be used to bring the auxiliary laser intooptical alignment. One such arrangement is a variable-position foldmirror 21, 21′ (FIGS. 2, 3 and 5); however, for simultaneous operationsas noted earlier such a mirror can be replaced by a beam splitter, e. g.a polarized one for maximum radiation transfer, or by spectral-band-wisesplitting devices such as dichroic filters.

The sensor system is ordinarily located on a host (FIG. 4). Anappropriate host is readily selected to optimize use of the inventionfor particular applications. In preferred embodiments, the host can be avehicle including an automobile or truck, sea vessel, airplane,spacecraft, satellite or projectile, or even simply a human or animal ortheir paraphernalia. Hosts are not limited to these examples, but canbasically consist of any carrier—even a stationary one—capable ofsupporting and maintaining the sensor, and exposing it to various kindsof articles or objects.

The sensor method or system specifications can vary and be optimized foruse in particular applications. One of ordinary skill in the art canselect preferred configurations of the system to suit a particularapplication. In preferred embodiments of the invention, the system canmonitor a field of regard at approximately 10 Hz frame rate—evidencingthe excellent sensitivity of the invention at high frequencies. Theinvention is capable, however, of monitoring in a range on the order of1 Hz to 1 kHz—or even 10 kHz, depending on size of articles of interest,and the detector field of view. Overall, the invention provides a highdegree of angular accuracy in determining the approach path of anincident ray.

Plural such sensor systems can be grouped and coordinated to provide upto 4π steradian coverage—i. e., for sensing in all directions at once.This kind of observation is appropriate for a host that is in the air orin outer space, and in some circumstances for a host that is waterborne.For a host on land, and for a water-surface-craft host in othercircumstances (particularly, no need to monitor below the water surface)2π steradian coverage ordinarily is entirely sufficient.

The sensor of the invention has the ability to monitor wavelengthsranging from ultraviolet (UV) to infrared (IR), particularly up to themidIR range.

Typically a MEMS mirror is limited in range to plus-or-minus ten tofifteen degrees about one or two orthogonal axes, i. e. through anoverall excursion 16 of roughly 20° (FIG. 5) to 30° for each axis. Inpreferred embodiments of the invention, as noted earlier, a lensassembly 14 is advantageously used to significantly increase this rangeoptically.

Most preferred embodiments of the invention eliminate the use of largeexternal scan mirrors and gimbals; as a result the invention is morerugged, and yet actually less expensive and several orders lighter andmore compact than conventional sensor systems. For example, the size ofthe system, depending on the application, is on the order of onemillimeter, or less, to a few centimeters rather than on the order ofone centimeter to tens of centimeters as described earlier forconventional units.

Dimensions of an oscillating scan mirror 15 may be, merely by way ofexample, in a range from a few tens of microns wide to severalmillimeters or more; such a mirror may be roughly square, or may have ahigh aspect ratio such as 25:1 or 50:1. Nominally and ideally, however,the aspect ratio should be approximately the square root of two, sincethe mirror surface—when at the center of its range of excursions—isinclined at 45° to both the incident and reflected beams. Accordinglythe most preferable tested embodiments use e. g. silicon scan mirrors inthe range of 1.5×2.1 mm (note that 1.5√{square root over (2)}=2.1); butagain these dimensions are not at all limiting. Such a mirror typicallyrotates about its own axis with an excursion in the range of ±1° to±10°—or even ±15° as previously noted.

The system mass can be made just one-tenth to one kilogram, alsogenerally several orders of magnitude lower than that of comparableknown devices. Angular resolution is readily placed in thesubmilliradian or even tens-of-microradians range, i. e. less than threeminutes of arc or even under one minute, versus the previously notedtens to hundreds of milliradians (two-thirds of a degree to tens ofdegrees) for sensors heretofore. Yet another major and remarkableadvantage of the invention is that the system can eventually useoff-the-shelf technology, requiring no expensive custom parts orinstrumentation.

Initially, the most highly preferred embodiments of the invention callfor a custom MEMS mirror array of at least 5×5 mirrors—and morepreferably 10×10 and even 30×30 mirrors—each individual mirror being1.5×2.1 mm, and with an afocal lens assembly that follows custom opticalspecifications but is otherwise conventionally fabricated. It isanticipated that these component designs will quickly become standard inthe field, and very shortly be available as commercial off-the-shelfunits.

Remarkably, even though the present invention achieves far finerresolution than earlier sensors, at the same time it nevertheless alsoprovides much broader effective field of regard. These dual advantagescan be stated together in terms of an extremely high effective dynamicrange.

The invention can redirect a new beam 43 (FIG. 3) of light (usuallygenerated locally—i. e. on the same platform) laterally for guidance ofany objects away from the host. The invention can also providedetermination of wavelength λ and frequency-modulation information f(t)in the received beam, so that those characteristics of the received rayscan be mimicked 41 in the new beam—which is relayed to another location,either for communications purposes or to lead an approaching object to adifferent destination. Alternatively the new beam can be directed backalong the same path 38 as received rays 13, to the extent that the fieldof regard of the optical system (or of the system together with othersuch optical systems being operated in parallel) is broad enough toprovide appropriate directions for the new beam. These capabilities areentirely beyond those of the prior art.

Preferred embodiments of the method of the invention, corresponding tothe apparatus discussed above, include the steps or functions of:

-   -   detection and angular location of a light source (FIG. 1),    -   determining characteristics of the received radiation (FIG. 2),        and    -   response (FIG. 3).

The first of these functions preferably includes these constituentsteps:

STEP 1—Incident rays 13 from a light source 1 illuminate the system, onits host platform, at a relative angle θ_(X), θ_(Y).

STEP 2—An afocal lens assembly 14 reduces a collimated or nominallycollimated incident or exiting ray angle, θ_(X), θ_(Y) (i. e., outsidethe optical system) by the ratio of the two focal lengths designed intothe assembly, 1:3 in this example, resulting in much smaller off-axisangles of θ_(X)/3, θ_(Y)/3 inside the optical system 10—i. e. at thescan mirror or mirrors 15. This arrangement is optimal to effectively,or virtually, bring the incident rays within the native scan range ofthe MEMS scan system.

The lens assembly 14 is described as “afocal” because it is not used tofocus the incoming rays directly onto the detector 24; rather theprimary lens 45 forms (inside the lens assembly) only a virtual image44, which the secondary lens 46 then recollimates—but only if theincoming beam 13 a, 13 is itself at least approximately collimated—toproduce substantially parallel rays in the beam approaching the detectorassembly 22.

STEP 3—The MEMS scan mirror continuously raster-scans the field ofregard. When the MEMS scan mirror intercepts laser energy at thecorresponding original angles θ_(X), θ_(Y) (and reduced angles θ_(X)/3,θ_(Y)/3), the detector detects the energy and in turn transmits thesignal to the control processor. The relative position reported at thatsame instant by the MEMS scan mirror assembly, and thereforecorresponding to θ_(X), θ_(Y) is recorded by the control processor 26.To enable this result, a conventional two-axis angle sensor (not shown)that measures shaft angle of the MEMS mirror has been precalibrated toprovide the corresponding field of regard angle (θ_(X), θ_(Y)) relativeto the optical axis.

STEP 4—The 2-D detector is fitted with a reimaging lens that focuses theincident beam at its conjugate location on the detector, relative to thesystem axis, provided that (1) the MEMS scan mirror is at an appropriateangle to direct the beam into the detector field of view, and (2) theincoming beam, within the envelope of extreme captured rays 13, 13 a(FIG. 5), is collimated or very nearly so. This arrangement tends tosomewhat diffuse the image of relatively nearby sources on the detector,and thus limit the response to light from relatively remote sources.

The detector is thus aided in essentially disregarding illumination fromnearby sources, which for purposes of preferred embodiments of thepresent invention are deemed to be most-typically irrelevant. (As willbe understood, contrary assumptions can be implemented instead, ifdesired, in other—generally conventional—optical trains.) Such exclusionof illumination that is not of interest, however, is generally secondaryin relation to other selective features in the system—e. g. spectralfiltering 21, 55, and a. c. signal filtering 56 or other arrangementsfor enhancing sensitivity to anticipated known modulation patterns.

The position-sensing detector next comes into play, sensing not onlypresence of the illumination but also the displacements ΔX, ΔY of itsfocal point (conjugate location) from the optical axis—and generatingcorresponding ΔX, ΔY signals for transmission to the control processor.

STEP 5—Mirror-bias commands Δθ_(X), Δθ_(Y), proportional to the ΔX, ΔYvalues, are generated by the control processor and sent to the MEMSscan-mirror assembly. These signals drive the conjugate locationapproximately to the optical axis; and as that location approaches theaxis the error signals ΔX, ΔY become progressively more linear andstable, by virtue of the inherent behavior of the PSD 24, so that theeventual determination of incident-beam location is extremely precise,accurate, and stable. At each instant the source angles outside theoptical system are related to the coordinates on the PSD surface by thefinal-stage focal length, i. e. each angle Δθ_(X) or Δθ_(Y) equals thecorresponding ΔX or ΔY coordinate divided by the 2-D detectorimaging-optic focal length f_(D) (FIG. 5)—subject to the angle-scalingeffect of the afocal assembly 14, discussed at “step 2” above.

STEP 6—The Δθ_(X), Δθ_(Y) incident-ray relative position as thenmeasured by the MEMS scan-mirror local angle sensors are made available,for later functions, as an accurate line-of-sight location of theincident ray relative to the system axis.

The second function of the system basically includes determining thewavelength and any accompanying temporal or spectral modulation of theincident ray or signal. Continuing the above sequence:

Step 7—A fold mirror 21 (FIG. 2) rotates to direct the incident beam 13to a spectrometer or photodiode 31. The fold mirror is basically asimple, motorized mirror that redirects light; but in other preferredembodiments this mirror can be replaced by a MEMS mirror or, as notedearlier, a beam splitter. One or more splitters, in tandem asappropriate, are particularly advantageous to permit simultaneousoperations of different types, e. g. detection, spectral analysis,imaging, distance probing, or active response—and combinations of these.

Step 8—A spectrometer 31 determines the incident ray wavelength; andeither the detector in the spectrometer acquires any temporal orspectral intensity or wavelength or temporal modulation to be detectedand sent 32 to the control processor. Portions of this task may beassigned to the PSD 24, filter 56 (FIG. 1) and processor 26 for dataacquisition during earlier steps 5 and 6.

The third system function is most typically an optical response that cantake any of several forms. One such form (FIG. 3), which makes use ofthe directional information collected in the first function, isgeneration and projection of a very bright beam of radiation oppositethe incident ray, to temporarily dazzle or confuse an operator oraiming-control apparatus at the source. Again continuing from thefirst-function sequence:

STEP 7—The fold mirror 21 (FIG. 3) rotates from its earlier positions21′ to align a powerful laser 34 along the optical axis, and therebyalong the known path to the source.

STEP 8—The laser transmits a temporarily blinding beam 35-38 in adirection opposite the incident rays 13, but back along the same path,in response to a command 33 from the control processor 26.

A fourth function uses the information collected in the second functionto generate and project a precisely wavelength-matched andtemporal-modulation-matched beam to a nearby location, preferably onethat progressively moves away from the host position, to draw any guidedobject away from the host. Friendly as well as hostile guided rendezvouscan be facilitated in this way. This fourth function includes issuanceof a processor command 41 (FIG. 3)—with necessary data λ, f(t)—to theauxiliary light source, e. g. tunable modulated laser 42. Atsubstantially the same time the determined information is advantageouslytransmitted (preferably as interpreted, encoded data) to a remotestation to document, e. g. for subsequent refined avoidance, what hasoccurred.

As will be understood, if the application at hand calls for directing abeam into the originally searched input volume 11, rather than alocation laterally offset from that volume, then instead of theauxiliary laser 42 it is possible to use the previously mentioned laser34—i. e., the one that can be aligned with the main optical path throughthe lens assembly 14. This option is particularly practical in the caseof a plural-sensor-system apparatus configured to scan 2π or 4πsteradians as previously discussed. In such applications essentially alllocations are within the scanned range of at least some one of thecomponent sensor systems.

A complex of other possible responses, and alternative applications ofthe information gathered in the first two functions, is within the scopeof the invention (FIG. 4). One such response is initiation of a distanceprobe operation to collect additional information about any such objectthat may be associated with the beam, or about facilities at the source,or both. Several of the references cited at the beginning of thisdocument provide very extensive information about distance-determiningcapabilities and design. Other ranging methods may be substituted asdesired. This form of the invention can also be used for any of variousother applications, such as for example transmission of modulatedoptical signals for free-space laser communications.

For each of the various applications additional components may be added,such as additional processing capability for further processing data, anannunciator for alerting an operator or connecting to an alarm formonitoring the system, or robotics for performing additional functionsin response to the detection.

Particularly preferred applications, as shown, include use of the systemin a vehicle or other host for detection of objects, or use of thesystem as a guide for a laser communications telescope—for which thesystem “communicates” angular, wavelength, frequency-modulation (orother temporal modulation) or other information between two telescopes.Also included is use of the system for continuous observation purposessuch as recognition and location of emergency distress signals e. g. abeacon, or flares, or identification of approaching vehicles.

Furthermore the system can detect such light signals in outer space oreven through large bodies of water. Thus objects can be identified andlocated regardless of whether they are floating in space, under the seaor on land. Other beneficial uses will appear from the drawing; however,it is to be understood that FIG. 4 is not intended to be exhaustive; i.e., not all functions of the invention described and discussed in thisdocument appear in that drawing.

Because of the versatility of the system and its many functions, it hasa wide range of applications spanning industries as diverse astelecommunications, optics, automotive, marine, aerospace, continuingobservation, and search and rescue.

In a particularly preferred embodiment of the system, the sensor systemutilizes a two-axis scan mirror (FIG. 5) of dimensions 1.5×2.1 mm, withmechanical scan angle of plus-or-minus 10° to 15°—for a total excursionof 20° to 30°—about both axes. A two-axis scan mirror is not arequirement; a single-axis scan mirror with one-dimensional detector canbe substituted. Using a two-axis scan mirror with a 2-D detector,however, allows greater flexibility in detecting throughout a volume ordetecting in more than one dimension.

The ±10° or ±15° sweep 16, i. e. 20° or 30° full-excursion, of the MEMSmirror or mirrors 15 is doubled—by the effect of reflection—to produce a40° or 60° deflection of the beam at that point. The MEMS system, inturn, is behind a lens assembly whose focal-length ratio (typically 1:3)triples that 40° or 60° deflection to provide, typically, a 120° to 180°overall field of regard. The two-axis MEMS scan mirror, operating atapproximately four milliradians for approximately the magnification(again, typically three) times 2λ/d, repeatedly sweeps the full120°×120° volume at more than 10 Hz. This then is the frame rate for acomplete scan of that field of regard.

If a collimated or nominally collimated incident ray is directed towardthe host within this overall field of view, the ray is projected—throughits reimaging lens—onto the detector when the MEMS two-axis scanningmirror is at the corresponding angular position. The MEMS scan-mirrorcontrol system then drives the scan mirror to maintain the incident rayon the detector, ideally a position-sensing photodiode detector asdescribed earlier—and preferably at its center.

This detector provides positional closed-loop feedback to the scanmirror, driving the focal point to minimize the ΔX and ΔY coordinates.In other words the beam is driven to the native origin on thephotosensitive surface of the diode.

When in that condition, the angular positions of the mirror provide thecorresponding azimuth and elevation angles Δθ_(X), Δθ_(Y) of theincident rays—based on the corresponding error coordinates ΔX, ΔY at thedetector surface, and the corresponding known relative mirror angles asexplained earlier. Limiting uncertainty of the input collimatedlaser-beam angle is the limiting resolution of the 2-D detector dividedby the reimaging lens focal length f_(D).

In addition to illuminating the PSD, the system advantageously includesa multiposition relay mirror (or fold mirror etc.) to alternativelydirect the incident beam to other detectors such as a spectrometer usedto determine incident-ray wavelength—or a beam-splitter to do soconcurrently. If preferred, quad cells, focal plane arrays, or linearrays such as a charge-coupled device (CCD) or other light sensitivearrays can be used instead. Ideally each individual detector of an arraycan be provided with its own individual microlens. Nevertheless thepreviously mentioned quantization effect remains a concern, and arraydetectors are generally slower than PSDs, particularly when taking intoaccount the necessary algorithmic procedures for readout andinterpretation of optical signals.

The same multiposition mirror can also serve to route output rays, froman onboard laser or other bright lamp, back along the original opticalpath toward the source of the initially detected incident beam—to blindthe source operator, or locate the source facility, or communicate withit, all as set forth earlier.

In practice of many of the preferred embodiments of the invention—butparticularly for situations in which the system cannot lock on to anactive source, usually because no active optical source is present ornone is being concurrently detected and tracked—it is especially helpfulto provide a vibration-sensing subsystem 57 (FIGS. 1 and 2) adjacent tothe scan mirror or mirrors, and a correctional-data path 58 for flow ofvibration information from the outputs of these sensors to the mainprocessor. (Although included in FIG. 1, such provisions most typicallyare in order only when no positional detection is available, e. g. as inFIG. 2 with the detector 24 out of service, or absent. Vibration sensing57, 58 and input filtering 55, 56 are omitted from FIGS. 3 and 5 only toavoid further clutter in those drawings.) This sensing module 57 withits correction path 58 enables a spectrometer, or an imaging system ordistance-determining system, that is part of the invention embodimentsto form a stable, high-resolution 2-D or 3-D image despite vibration inthe host platform.

Most typically the vibration sensor includes a gyroscope or set ofaccelerometers, separated by known lever arms. These devices provideenough information—most typically with respect to five degrees offreedom—to enable the system to incorporate compensating maneuvers ofits moving mirrors, canceling out the effects of such vibration. Thesedevices should be augmented by a GPS sensor for geodetic coordinates

Sensing elements 57 positioned along the plane of a supporting base ofthe moving mirror or mirror assembly 15 can for example include threelinked accelerometers sensitive to motion normal to that plane, and twoothers sensitive to motion within that plane—ordinarily but notnecessarily parallel to orthogonal edges of the base. Suchvibration-sensing devices in effect define instantaneous characteristicsof any host-platform vibration. Such sensing subsystems in themselvesare well known and conventional. The data they produce must flow to theprocessor 26 and be interpreted promptly enough to enable effectivefeedback into the control circuits of the moving mirror or mirrors, toachieve cancellation within the desired imaging accuracy of the overallsystem.

For most purposes of the present invention, as previously mentioned,raster scans are advantageously performed using a spiraling pattern 59(FIG. 6). With moving mirrors, executing such a pattern is mosttypically far more energy-efficient and fast than tracing amore-conventional rectangular-envelope serpentine pattern. For optimumspeed and efficiency the sequence reverses direction at each end—i. e.,outward in one scan, inward in the next, and so forth. As in any rasteroperation, the number and pitch of the spiral revolutions should beselected with care to obtain good resolution without significant gaps inthe image.

In accompanying apparatus claims generally the term “such” is used(instead of “said” or “the”) in the bodies of the claims, when recitingelements of the claimed invention, for referring back to features whichare introduced in preamble as part of the context or environment of theclaimed invention. The purpose of this convention is to aid in moreparticularly and emphatically pointing out which features are elementsof the claimed invention, and which are parts of its context—and therebyto more distinctly claim the invention.

The foregoing disclosure is intended to be merely exemplary, and not tolimit the scope of the invention—which is to be determined by referenceto the appended claims.

1-95. (canceled)
 96. An optical system for dynamically determiningradiation characteristics, including associated angular directionthroughout a specified range of angular directions, of an externalarticle in a volume outside the system; said optical system comprising:an optical detector; an entrance aperture; an afocal element, associatedwith the aperture, for enlarging the field of regard of such externalarticle and such volume as seen by the detector; and disposed along anoptical path between the detector and the entrance aperture, at leastone mirror, rotatable about plural axes, for causing the detector toaddress varying portions of such volume outside the optical system; eachmirror of the at least one mirror having dimensions in a range fromthirty microns to five millimeters; wherein, due to said enlarging ofthe field of regard together with rotation of the at least one mirror,such external article is visible to the detector throughout thespecified range, substantially without changing magnitude of saidenlarging.
 97. The optical system of claim 96, wherein: each mirror ofthe at least one mirror is a microelectromechanical mirror.
 98. Theoptical system of claim 96, wherein: the afocal element is an afocallens assembly disposed at the aperture, and amplifies the varyingintroduced by the at least one mirror.
 99. The optical system of claim98: wherein the afocal lens assembly does not focus such externalarticle onto any solid element of the optical system; and furthercomprising a focusing lens, associated with the detector, for:intercepting a radiation beam that has passed through the afocal lensassembly, and that also has been reflected by the at least one mirror,and focusing rays, in said radiation beam, from such external articleonto the detector.
 100. The optical system of claim 96, wherein: theafocal enlarging element is disposed generally at the aperture.
 101. Theoptical system of claim 96, wherein: the afocal enlarging elementdefines the aperture.
 102. The optical system of claim 96: furthercomprising an imaging module; and wherein the afocal enlarging elementand the at least one mirror are shared by both: the imaging module, andthe detector with its focusing lens.
 103. The optical system of claim96: further comprising a spectral-analysis module; and wherein theafocal enlarging element and the at least one mirror are shared by both:the spectral-analysis module, and the detector with its focusing lens.104. The optical system of claim 96: further comprising an auxiliaryoptical system that includes at least one of: a ranging laser forprojecting a ranging beam to such article, and a ranging-laser receivingmodule, distinct from the aforesaid detector with its focusing lens, forreceiving and analyzing the ranging beam after reflection from sucharticle; and wherein the afocal enlarging element and the at least onemirror are shared by both: one or both of the ranging laser andreceiving module, and the detector with its focusing lens.
 105. Theoptical system of claim 96: further comprising an auxiliary opticalsystem that includes at least one of: a communication-beam transmissionmodule for transmitting a first modulated communication beam toward sucharticle, and a communication-beam reception module, distinct from theaforesaid detector with its focusing lens, for receiving andinterpreting a second modulated communication beam received from sucharticle or from a region of such volume that includes such article; andwherein the afocal enlarging element and the at least one mirror areshared by both: one or both of the transmission and reception modules,and the detector with its focusing lens.
 106. The optical system ofclaim 96: further comprising an auxiliary optical system that includesat least one of: a communication-beam transmission module fortransmitting a first modulated communication beam toward such article,and a communication-beam reception module for receiving and interpretinga second modulated communication beam received from such article or froma region of such volume that includes such article; and wherein theafocal enlarging element and the at least one mirror are shared by oneor both of the transmission and reception modules.
 107. The opticalsystem of claim 96: further comprising a powerful laser for projecting abeam to impair function or structural integrity of such article; andwherein the afocal enlarging element and the at least one mirror areshared by both: the powerful laser, and the detector with its focusinglens.
 108. The optical system of claim 96: further comprising a laserfor dazzling or confusing either a human operator or optical apparatusassociated with such article, or both; and wherein the afocal enlargingelement and the at least one mirror are shared by both: the dazzlinglaser, and the detector with its focusing lens.
 109. The optical systemof claim 96: wherein the detector reports relative location of incidentradiation on a sensitive surface of the detector; and further comprisingmeans for automatically responding to the detector by activelyservocontrolling the at least one mirror to substantially center animage of a detected source on the detector.
 110. The optical system ofclaim 109, wherein the external article comprises a radiation source ofa particular type, said characteristics comprise existence and presenceof the source, and the optical system is for detecting the source anddetermining its angular location, and: said optical detector is adetector for such radiation from such source of such particular type;and further comprising means for automatically responding to thedetector by actively servocontrolling the at least one mirror tosubstantially center an image of a detected source on the detector. 111.The optical system of claim 110, further comprising: means for readingand interpreting angular position from mirror position feedback signalswhile the image is substantially centered on the detector.
 112. Theoptical system of claim 111, wherein: the responding means comprisemeans for continuing to servocontrol the at least one mirror to trackthe already-detected source substantially at the detector center. 113.The optical system of claim 112, wherein: the at least one mirrorcomprises plural mirrors; and the continuing means comprise means forusing one or more mirrors to track the already-detected source, and oneor more other mirrors to instead simultaneously perform anotherfunction.
 114. The optical system of claim 113, wherein: the otherfunction comprises searching for another source, previously not yetdetected.
 115. The optical system of claim 113, wherein: the otherfunction comprises operating the auxiliary optical system with respectto said already-detected source or another article or scene.
 116. Theoptical system of claim 112, further comprising: operating abeam-splitter to enable use of an auxiliary optical system, with respectto said already-detected source or another article or scene,simultaneously with said continuing tracking of the already-detectedsource.
 117. The optical system of claim 96, wherein: the detector is aposition-sensing detector (PSD).
 118. (The optical system of claim 96,wherein: the detector is a quad cell.
 119. The optical system of claim96, further comprising: means for substituting a detector array for thedetector, to image the already-detected source or associated articles,or both.
 120. The optical system of claim 96, further comprising: meansfor directing a response toward the detected article or an articleassociated therewith, or both.
 121. The optical system of claim 120,wherein: the response-directing means comprise means for emitting a beamof radiation that uses said entrance aperture as an exit aperture and isreflected from said at least one mirror; wherein the response-directingmeans share, with such radiation from such source, both: said entranceaperture, and said at least one mirror.
 122. An optical system fordynamically determining radiation characteristics, including associatedangular direction, of an external article in a volume outside thesystem; said optical system comprising: an optical detector; an entranceaperture; an afocal optically powered element, associated with theaperture, for enlarging the field of regard of such external article andsuch volume as seen by the detector; and wherein the afocal element doesnot focus such external article onto any solid element of the opticalsystem; disposed along an optical path between the detector and theentrance aperture, at least one mirror, rotatable about plural axes, forcausing the detector to address varying portions of such volume outsidethe optical system and with the enlarged field of regard produced by theafocal element; a focusing lens, associated with the detector, for:intercepting a radiation beam that has passed through the afocalelement, and that also has been reflected by the at least one mirror,and focusing rays, in said radiation beam, from such external articleonto the detector; wherein the afocal element and mirror cooperate withthe focusing lens and detector, to image such article onto the detector.123. The optical system of claim 122, wherein: the afocal enlargingelement is disposed generally at the aperture.
 124. The optical systemof claim 122, wherein: the afocal enlarging element defines theaperture.
 125. The optical system of claim 122: further comprising animaging module; and wherein the afocal enlarging element and the atleast one mirror are shared by both: the imaging module, and thedetector with its focusing lens.
 126. The optical system of claim 125,wherein: each mirror of the at least one mirror has dimensions in arange from thirty microns to five millimeters.
 127. The optical systemof claim 122: further comprising a spectral-analysis module; and whereinthe afocal enlarging element and the at least one mirror are shared byboth: the spectral-analysis module, and the detector with its focusinglens.
 128. The optical system of claim 127, wherein: each mirror of theat least one mirror has dimensions in a range from thirty microns tofive millimeters.
 129. The optical system of claim 122: furthercomprising an auxiliary optical system that includes at least one of: aranging laser for projecting a ranging beam to such article, and aranging-laser receiving module, distinct from the aforesaid detectorwith its focusing lens, for receiving and analyzing the ranging beamafter reflection from such article; and wherein the afocal enlargingelement and the at least one mirror are shared by both: one or both ofthe ranging laser and receiving module, and the detector with itsfocusing lens.
 130. The optical system of claim 129, wherein: eachmirror of the at least one mirror has dimensions in a range from thirtymicrons to five millimeters.
 131. The optical system of claim 122:further comprising an auxiliary optical system that includes at leastone of: a communication-beam transmission module for transmitting afirst modulated communication beam toward such article, and acommunication-beam reception module, distinct from the aforesaiddetector with its focusing lens, for receiving and interpreting a secondmodulated communication beam received from such article or from a regionof such volume that includes such article; and wherein the afocalenlarging element and the at least one mirror are shared by both: one orboth of the transmission and reception modules, and the detector withits focusing lens.
 132. The optical system of claim 131, wherein: eachmirror of the at least one mirror has dimensions in a range from thirtymicrons to five millimeters.
 133. The optical system of claim 122:further comprising a powerful laser for projecting a beam to impairfunction or structural integrity of such article; and wherein the afocalenlarging element and the at least one mirror are shared by both: thepowerful laser, and the detector with its focusing lens.
 134. Theoptical system of claim 133, wherein: each mirror of the at least onemirror has dimensions in a range from thirty microns to fivemillimeters.
 135. The optical system of claim 122: further comprising alaser for dazzling or confusing either a human operator or opticalapparatus associated with such article, or both; and wherein the afocalenlarging element and the at least one mirror are shared by both: thedazzling laser, and the detector with its focusing lens.
 136. Theoptical system of claim 135, wherein: each mirror of the at least onemirror has dimensions in a range from thirty microns to fivemillimeters.
 137. The optical system of claim 122: wherein the detectorreports relative location of incident radiation on a sensitive surfaceof the detector; and further comprising means for automaticallyresponding to the detector by actively servocontrolling the at least onemirror to substantially center an image of a detected source on thedetector.
 138. An optical system for dynamically determining radiationcharacteristics, including associated angular direction, of an externalarticle in a volume outside the system; said optical system comprising:an optical detector; an entrance aperture; an afocal optically poweredelement, disposed generally at the aperture, for reducing the field ofregard of such external article and such volume as seen by the detector;and wherein the afocal reducing element does not focus such externalarticle onto any solid element of the optical system; disposed along anoptical path between the detector and the entrance aperture, at leastone mirror, rotatable about plural axes, for causing the detector toaddress varying portions of such volume outside the optical system andwith the reduced field of regard produced by the afocal reducingelement; a focusing lens, associated with the detector, for:intercepting a radiation beam that has passed through the afocalreducing element, and that also has been reflected by the at least onemirror, and focusing rays, in said radiation beam, from such externalarticle onto the detector; wherein the afocal reducing element andmirror cooperate with the focusing lens and detector, to image sucharticle onto the detector.
 139. The optical system of claim 138: furthercomprising an auxiliary optical system that includes at least one of: acommunication-beam transmission module for transmitting a firstmodulated communication beam toward such article, and acommunication-beam reception module, distinct from the aforesaiddetector with its focusing lens, for receiving and interpreting a secondmodulated communication beam received from such article or from a regionof such volume that includes such article; and wherein the afocalreducing element and the at least one mirror are shared by both: thedetector with its focusing lens, and one or both of the transmission andreception modules.
 140. The optical system of claim 138, wherein: eachmirror of the at least one mirror has dimensions in a range from thirtymicrons to five millimeters.
 141. The optical system of claim 138:wherein the detector reports relative location of incident radiation ona sensitive surface of the detector; and further comprising means forautomatically responding to the detector by actively servocontrollingthe at least one mirror to substantially center an image of a detectedsource on the detector.
 142. The optical system of claim 138: furthercomprising an auxiliary optical system that includes an imagingreception module, distinct from the aforesaid detector with its focusinglens, for receiving and interpreting an image beam received from sucharticle or from a region of such volume that includes such article; andwherein the afocal reducing element and the at least one mirror areshared by both: the detector with its focusing lens, and the imagingreception module.